Turbine construction



tag. 24, 1943.

H. ZSCHOKKE TURBINE CONSTRUCTION Filed March 24, 1.941

tented Aug. 24, N43

TURBINE CONSTRUCTION Hans Zschokke, Zurich, Switzerland, assignor to Aktiengesellschaft Baden, Switzerland Brown,

Boverl & Cie.,

Application March 24, 1941, Serial No. 385,036

a In Switzerland March 26, 1940 1 Claim.

This invention relates to the construction of steam or gas turbines, and is concerned particularly with improvements in the spacers for the blades of steam or gas turbines-that are exposed to motive fluids oi especially high temperatures.

It is known that in turbines, especially turbines impelled with very high temperature motive fluids, considerable differences in lengthwise expansion are encountered at times due to difl'erent heating of the blades and the blade carrying members, but above all, however, continuously also with uniform heating due to the physical differences, necessary for structural reasons, in the materials of the blades and of the blade carrying members. These differences in lengthwise expansion occur because the austenitic, highly alloyed steel of the blades has a much greater coefilcient of expansion than has the martensitic, lower-alloyed structural steel of the blade carrying members; in this way there result pressure stresses in the roots of the blades and in the spacers, and tensile stresses in the blade carrying members, that lead to permanent deformations and to loosening of the blades. Under certain conditions, to the heat expansions just mentioned are added expansions in the rotor due to centrifugal forces that act in the same direction.

It has now been found that these drawbacks may be avoided, according to the present invention, by using as the structural material for the spacers a material which has a lower coefllcient of expansion than has the structural material of the blade carrying member. In this way it is possible to reduce the total heat expansion of the blading over the periphery and with equal heating of the blades and blade carrying members to keep the expansion of the blade roots and of the spacers, together, equal to, or less than, the expansion of the blade carrying members. Furthermore in the event that the blades attain a higher temperature than the blade carrying member, by means of a suitable choice as regards composition of the material for the spacers and a correct ratio of blade root thickness to spacer thickness the extra expansion will only produce compressive stresses which remain within the elastic limit of the structural material concerned, so that permanent deformations and resulting slackening of the blades are prevented, and in the case of uniform temperature of the blading and blade carrying member, due to the same total heat expansion, temperature stresses no longer occur. Similarly the total expansion of the blade row can be so adjusted that possible expansion of the blade carrying member due to centrifugal forces can also be taken into account.

The blade roots and spacers are to have as nearly equal thickness as possible, in the direction of the periphery, throughout the whole width of the blade, so that their" total expansion becomes the same in the direction of the periphery over the whole width of the blade. The centrifugal forces of the blade of course determine the least dimension of the blade root.

In the following, the expansion coefflcients of the steels under consideration. and suitable spacer alloys are mentioned. For a temperature range from 20 C. to about 600 0., they are as follows: 1

Slightly alloyed structural steel for It has been found that chromium steels having chromium contents of from about 10% to about 35% (remainder, iron), and nickel-iron alloys having nickel contents of from about 20% to (remainder, iron), are suitable as structural materials out of which to form the spacers.

In the appended drawing,

Fig. l is a partial section of a blade-carrying member with a blade in elevation;

Fig. 2 is a cross-section of a spacer adapted to co-operate with the blade and blade-carrying member shown in Fig.1;

Fig. 3 is a right cross-section of the blade shown in Fig. 1;

Fig. 4 is a radially cross-sectional View of a Curtis wheel showing impulse blades rooted in the periphery of the wheel;

Fig. 5 is a fragmentary plan view of Fig. 4, with impulse blades removed; and

Fig. 6 is a cross-sectional view taken on line A-B of Fig. 4.

In Figs. 1 to 3 inclusive of the appended drawing, a is a reaction blade, b is a spacer and c is a blade carrier. Blade carrier c may be either a stator (in which event a. is a guide blade) -or a rotor (in which event a is a running blade).

In Figs. 4 to 6 inclusive, 0 is the blade carrier of a Curtis wheel with impulse blades (11, a2, spacers b (Fig. 6) and end pieces d1, dz, these latter penetrating the crown, e, of the wheel and being riveted in position. Special openings f1, is. are provided to enable the blades a1, ac, to be inserted in the grooves or, 0:, together with the intermediate spacers, in the manner described in U. 8. Patent No. 930,735 to J. Dahl.

I claim:

A rotor for a steam or gas'turbine, said rotor including an annular metallic blade-carrying member, a plurality of metallic rooted blades mounted on the periphery of said blade-carrying member and a plurality of metallic spacers for spacing the blades about the periphery of the blade carrying member, wherein the blade roots and the spacers have substantially equal thicknesses in the direction of the periphery of 1 tural steel having a coefllcient of expansion of about 14-15 x 10- the metal oi! the blades is an austenite steel-having a coeflicient o1 expansion 0! about 17-19 x 10-, and the metal of the spacers is selected from the group consisting of such chromium steels containing from about 10 to about 35% chromium with remainder iron as have coeflicients of expansion from about 11 x 10- to about 12 x 10- and such nickel steels containing from about 20 to about 60% nickel with remainder iron as have coeiiicients of expansion 01 approximately 8.5 x 10-, whereby the expansion of the blade roots and spacers, together, is maintained at a value not greater than that of the blade-carrying member.

HANS ZSCHOKKE. 

